1. Field of the Invention
Bleaching stilbene yellow.
2. Summary of the Invention
At the present time it is considered environmentally sound to repulp paper for reuse. One type of paper that may be reused is the yellow pages of telephone books. One of the stilbene yellow dyes is the dye that is used to color these pages. At the present time the sole reuse of these pages is as a furnish for new yellow pages since it has not been possible to remove the yellow color.
One of the reasons for this is that the exact composition of the stilbene yellow dyes is considered to be unknown or undetermined. This is the statement given in the Chemline Databank.
It has now been found that chlorine dioxide is a specific bleaching agent for stilbene yellow dye. Concentrations of chlorine dioxide as low as 0.25% up to 4% based on the oven dry weight of the paper fiber are enough to bleach the stilbene yellow. Other bleaching agents have been tried and do not bleach the dye.